Fluid power transmission



1951 s. M. DARLING 2,968,623

FLUID POWER TRANSMISSION Filed July 25, 1956 [-vION Qu. NO

I I E 0: Lu CL 2 Lu III IIIIIIIIII L I nss ALISOOSIA INVENTOR.

SAMUEL M DARLING h is A T TORNE Y5 United States Patent FLUID POWER TRANSMISSION Samuel M. Darling, Lyndhurst, Ohio, assignor to The Filed July 25, 1956, Ser. No. 600,020 3 Claims. (Cl. 252--75) This invention relates to fluid power transmission and to a power transmission fluid characterized by an ASTM slope below 03, comprising a light mineral oil of normal viscosity index, and an inorganic gelling agent, imdazoline and aliphatic amine in amounts to impart an ASTM slope of below 0.3 to the mineral oil.

Petroleum oils have certain performance characteristics which make them particularly suitable for use as power transmission fluids. A power transmission fiu d wh'ch is well suited for the job for which it is intended must .have good flowability and pumpability, lubricating ab'lity, chemical stability, rust-inhibiting ab'lity, demulsibIlity, and defoaming ability. All of these character'stics a e important, and should be displayed over the entire range of temperatures at which the system is to be used. All fluids, however, undergo a change in viscosity with temperature. The rate of change of viscosity wth change in temperature which characterizes petroleum oils is not as low as that for many synthetic oils such as silicone oils and the Uc-on oils, which are polypropylene glycol ethers, and this is a disadvantage.

The rate of change in viscosity with temperature of petroleum oils ordinarily is measured by the vis osity index, usually abbreviated V1. The h'gher the V.I., the lower the rate of change in viscosity, and the better the petroleum oil for use as a hydraulic fluid. However, the viscosity index loses its sensitivity a a cha acterizing property when the oil has an exceptionally low rate of change in viscositv, of he order of that which characterizes many synthetic oils. A viscosity temperature relationship has been developed which is su erior to the viscosity index for this type of petroleum 0'1. Th s is the ASTM slope, adopted as a standard method by the American Petroleum Institute, Standard 533-43, ASTM designation D-341-43. This slope is the angent of the acute angle of the viscositytemoerature plot of the oil on the ASTM standard chart D-341-43. The sma ler the ASTM slope, the flatter the curve, and the lower the change in viscosity with temperature.

' Typical ASTM slopes of a number of petroleum and synthetic oils are given below:

Viscosity, SSU Petroleum Oils A S'IM Slope 100 F. 210 F.

Straw Paratfin 74 1 36 6 0.78 Automatic Transmission Fluid 200 50 0. 66 Synthetic Oi s:

Silicone Oi s- Dow Cornin 550 440 101 0.45 General Electric 9981LT125 577 231 0. 23 Ucon Oils 385 75. 1 0. 55 525 93 l 0 51 LB 650-X 650 106 0. 51 Esters- Bis-(2-ethylhex l) sebacate.- 67.8 87 0.70 Bis-(3,5,5-trimethylhexyl) sebacate; 94. 6 41. 3 0. 65

Monobutyl poly 1,2-oxy propylene glycols. See Kirkpatrick U.S. No. 2,615,853.

The lighter mineral oils of low viscosity would be ,especially suitable for use as power transmission medza because of their low sludge and deposit-forming tendencies compared to the heavier oils. However, light oils lack lubricating ability under operating conditions, and ASTM slope is in most instances too high. In fact, the light oils have such a low viscosity at hgh temperatures that they are not suited without modification for such purposes.

ln accordance with this invention, power transmission fluids are provided having a viscosity within the range from to 1000 SSU at F. and from 50 to 750 SSU at 210 F., and an ASTM slope below about 0.3, employing as the base oil light lubricating oils having a viscosity of about 50 to 300 SSU at 100 F. and from 25 to 55 SSU at 210 F. The ASTM slope of the light lubrieating oils is not critical because the power transmission fluids of the invention nonetheless have an ASTM slope of less than 0.3, considerably less than many synthetic oils and most ordinary petroleum hydrocarbon oils, even when highly refined, as the above table shows.

The power transmission fluids of the invention comprise from 1 to 3% based on the weight of the oil of an inorganic gelling agent, from about 1% to about 60% by weight of the gelling agent of an aliphatic amine having an aliphatic radical of from 8 to 20 carbon atoms, and from 1 to about 20% by weight of the gelling agent of an imidazoline having an aliphatic radical of from 8 to 20 carbon atoms. These three additives in combination increase the viscosity of the light oil to the point where the composition has a viscosity suitable for a power transmission fluid, and in addition improve the ASTM slope of the base oil to below 0.3. The compositions of the invention are fluid under all conditions of use at normal and elevated temperatures.

These effects are not obtained in the absence of the inorganic gelling agent, imidazoline or aliphatic amine. The increase in the viscosity and decrease in the ASTM slope due to the inorganic gelling agent are relatively small. The aliphatic amine and imidazoline alone have no eflect upon viscosity or ASTM slope. However, in the presence of the inorganic gelling agent the aliphatic amine and imidazoline effect a further increase in viscosity, and a further decrease in the ASTM slope. Thus, the amine makes it possible to achIeve higher viscosities and lower ASTM slope within the desired ranges, using lesser amounts of the inorganic gelling agent. The imidazoline also tends to stabilize the composition aga'nst settling of the inorganic gelling agent. The viscosityincreasing and ASTM slope decreasing effects of the amine and imidazoline are obtained after the mixture of oils, gelling agent, imidazoline and amine have been heated to temperatures of 300 F. or higher.

The ubricatin oilstock used in preparing the compositions of the invention will have a viscosity within the range rcm S0 to 300 SSU at 100 F. and 25 to 55 SSU at 210 F. The base stock is preferably a lubricating oil fraction of petroleum and it may be unrefined, acid-refined or solvent-refined, as required for the particular lubricating need. The nature of the base oil makes little difference in the relative consistencies of the compositions, although conventionally acid-refined oils produce slightly thicker fluids than the solvent-refined oils. The viscosity index of the oil is not critical.

The inorganic gelling agent can be any inorganic material which is dispersible in the oil and which is so finely divided as to be nonabrasive. The preferred materials are the aerogels which can be formed from any material not incompatible with the oil, such as silica, alumina and magnesia. Other gel-forming metal oxides, hydroxides and sulfides can be used, of which attapulgite, the hentonites (such as Wyoming bentonite, montmorillonites and hectorite), beidellite, saponite, nontronite, sepiolite, biotite, vermiculite and zeolites, synthetic clays such as magnesia-silica-sodium oxide, lime-silica-potassium oxide 3 and baria-silica-lithium oxide are exemplary, as well as synthetic zeolites, of which the complex aluminum silicates are exemplary.

A series of silica aerogels which can be used as the inorganic gelling agent of the invention are manufactured by Monsanto and marketed under the trade name Santocel.

Santocel C is prepared from an alkali silicate solution. Silicic acid dissolves in caustic alkali such as sodium hydroxide and the alkali silicates, such as sodium silicate, can be obtained from various natural minerals and clays or by fusing silicon dioxide with alkali hydroxides or carbonates. Fused alkali silicates such as water-glass, sodium tetrasilicate (Na Si O can be completely dissolved on long heating with water, but the result is not a solution of the silicate as such but of silicic acid peptized by alkali as well as free alkali. By addition of an acid to such a solution, for example, an inorganic acid such as sulphuric acid, hydrochloric acid or carbonic acid, or an organic acid such as acetic acid, oxalic acid or formic acid, the silicic acid is precipitated in the form of a gel which is called a hydrogel or aquogel. The structure of this gel has not been fully elucidated but it is generally accepted that it is composed of a honeycomb structure of the silicon dioxide SiO within the pores of which is enclosed the aqueous solution remaining after precipitation of the silicic acid. Thus, it can be generally stated that these hydrogels can be obtained starting from any watersoluble alkali silicate, including not only water glass as mentioned above but sodium metasilicate Na SiO sodium metasilicate nonahydrate Na SiO 9H O and sodium disilicate Na Si All of these silicates are soluble in water, in which they decompose to form silicic acid solution.

Such an aqueous solution of silicic acid will contain sufficient SiO in solution to form a hydrogel containing within the range from 3% to about 12% silica as SiO after gel formation by addition of the acid. The amount of silica can readily be calculated, depending upon the amount of acid which is required to acidify the solution and whether the acid employed is concentrated or diluted. It is not necessary to characterize the silicic acid solution in terms of the alkali content calculated either as Na O or NaOH inasmuch as this forms a salt with the anion of the acid employed and is washed. out of the aquogel at the time of alcogel formation.

After formation of the aquogel, the gel is washed free from salts and excess acid, and then converted to an alcogel by soaking in ethyl alcohol or some other watersoluble volatile aliphatic alcohol. Several portions of the alcohol may be necessary completely to remove the aqueous solution. The resulting alcogel then is placed in an autoclave. In order to remove the liquid phase without a collapse of the gel structure, the autoclave is heated at a temperature above the critical temperature of the alcohol, and the pressure is allowed to increase to a point above the critical pressure of the alcohol. The vent valve is then opened and the alcohol allowed to escape. Under these conditions the silica gel structure remains practically undisturbed and the liquid phase of the gel is replaced with air. The material is then reduced in particle size by blowing it through a series of pipes containing sharp bends with jets of compressed air. Santocel C has a secondary particle size of about three to five microns.

Santocel A is prepared as set forth for Santocel C up to the point of removal of the product from the autoclave. This material is run through a continuous heating chamher where it is heated for one-half hour to a temperature of about 1500 F. to eliminate the last traces of volatile material. It is then broken down in a reductionizer or micronizer to a particle size of about one-sixteenth inch in diameter. The SiO content of the original hydrogel used in preparing Santocel C is approximately 9.75%, whereas that of Santocel A is about 7.0%.

AR is a modification of A, differing only in that. the

material is reductionized to about the same particle size as C, approximately three to five microns in diameter.

ARD is a modification of AR, differing only in that ARD is densified by extracting air under vacuum, and there'Tore has a smaller volume than AR.

AX is an A which has not been devolatilized.

CD is a C which has been devolatilized as set forth for Santocel A. The Santocel is reductionized before being devolatilized.

CD R differs slightly from CD,, in that the CD R has been devolatilized just after heating in the autoclave and then reductionized. It differs from CD in that the latter is reductionized before being devolatilized.

The primary differences between the A and C series are as follows:

(1) The OS are prepared from a sodium silicate solution containing 25% more silica than the As. Therefore, in general the As are lighter and composed of smaller particles than the Us (2) The As have undergone a devolatilization step in their preparation.

The following are the bulk densities of several of the preferred silica aerogels:

Density, grams per ml.

AR ARD 0.056 to 0.064 C 0.082

In general, AR and ARD show'superior gelling ability and the As in general are better than the Cs. Silica aerogels which have been devolatilized generally have a higher gelling efficiency than the undevolatilized aerogels.

Other types of inorganic gelling agents which may be used include a Fumed Silica marketed by B. F. Goodrich Company. It is finely divided and appears very much like an aerogel. It is made by a combustion or vaporization process, as a source of white carbon black" for the rubber industry. The particles are several microns in size and porous in nature.

Another material is Linde Silica Flour marketed by Linde Air Products Co. It is very similar in physical appearance to the silica aerogel. The particle size of the silica is urported to be 0.01 to 0.05 micron and the silica is said to be manufactured by burning silicon tetrachloride and collecting the combustion product on cool plates analogous to the production of carbon black. The particles are thought to be aggregates or clusters of particles rather than of sponge-like character.

Still another inorganic gelling agent known is Ludox" silica from du Pont, which is known as a silica sol, and silica derivatives thereof. It has a particle size of the order of 0.01 to 0.03 micron.

The silicas from Columbia-Southern also are useful. These have the following properties.

Brunauer-Emmett- Teller Nitrogen Absorption Surface Area, int/gm.

Wet Screen Retained 325 Mesh, Percent 0.004. 257.0 0.01 236 5 n 02 ca. 210 0 0.008. 215 5 0.004- 228.0-

In preparing the compositions of the invention it 1s necessary to remove the water from the sol and replace it with an oil. This is possible by formulating the sol Any aliphatic saturated and unsaturated primary and secondary amine can be used. Those having aliphatic radicals of from eight to twenty carbon atoms are the most satisfactory. The primary amines will have one such radical, and the secondary amines two. The primary aliphatic amines are preferred. Typical are octylamine, decylamine, dodecylamine, stearylamine, palmitylamine, myristylamine, oleylamine, myricylamine, dioctylamine, methyl decylamine, octyl dodecylamine, butyl stearylamine, distearylamine, dilaurylamine, ethylnonylamine and dieicosylamine. Decylamine and dodecylamine are illustrated in the examples, but it will be understood that any member of this class of amines can be substituted therefor with satisfactory results.

The amine should not be volatile at the temperatures at which the lubricant is to be used, and accordingly usually has a boiling point above about 300 F. The amine should also be oil-dispersible or oil-soluble and will also be hydrophobic if it has a sufficiently long-chain aliphatic group, over about ten to twelve carbon atoms.

The imidazoline employed in the compositions of the invention has the following general structure:

H2C-CH2 5 4 R-N1 2 3N' where R is hydrogen, alkyl or a hydroxyalkyl radical having from one to eighteen carbon atoms and R is an alkyl or alkylene group having from eight to twenty carbon atoms.

These compounds are prepared by reaction of aliphatic acids and diamines followed by cyclization, in the following way:

HzC--CH2 l +2Hz0 R C O OH-l-RNH CHzCHzNHz'R-N N 1 where R and R are the same as in the general formula.

Illustrative R radicals are undecyl, tridecyl, pentadecyl, undecenyl, heptadecyl and heptadecenyl. Illustrative R radicals are ethyl, methyl, propyl, butyl, hexyl, hydroxyethyl, hydroxyisopropyl, hydroxybutyl and hydroxyhexyl.

The imidazoline should be oil-dispersible or oil-soluble and will also be hydrophobic in view of the long-chain alkyl group at the R position.

The relative proportions of the inorganic gelling agent and the oil will vary somewhat depending upon the desired viscosity in the final compositions, the gelling ability of the inorganic gelling agent and the viscosity of the oil used. Compositions made with the lower viscosity oils require a somewhat larger amount of inorganic gelling agent to give a composition of the same viscosity. The compositions of the invention are fluids. In general, the amount of inorganic gelling agent falls within the range of from 1 to 3% and in most cases preferably would be from 2 to 3%.

The viscosity, as might be expected, increases in a fairly linear relationship with increase in concentration of the inorganic gelling agent and the amount of gelling agent can be selected in relation to the desired viscosity in view of this.

The concentration of the amine will usually lie within the range from about 1% to about 60%, and the concentration of the imidazoline will usually lie within the range from about 1% to about 20%, preferably 5 to both based on the weight of the inorganic gelling agent, but here again the amounts employed will depend upon the increase in viscosity desired, the amount and nature of the gelling agent and the economics involved. A cheaper compound can of course be used in much larger quantities than an expensive compound at the same total cost of the composition.

The composition is made simply by mixing the inorganic gelling agent, the oil, the aliphatic amine and the imidazoline in any order or manner. The amine and imidazoline also can be incorporated with the inorganic gelling agent before mixing with the oil, for example, by dissolving them in a solvent such as pentane, mixing it with the gelling agent and then evaporating the pentane. Such a treating agent can be sold as an article of commerce and dispersed in an oil when the composition of the invention is to be prepared.

Generally, the amine and imidazoline are dispersed in the oil and the inorganic gelling agent added thereto and mixed therewith. Any simple mixing technique can be employed and if desired the mixture can be homogenized in a colloid mill or subjected to high shear by ejection or atomization through a small orifice such as a diesel injector nozzle, although this is unnecessary.

The amine and imidazoline must be uniformly dis tributed in the composition or on the inorganic gelling agent and for this reason the amine and imidazoline are oil-dispersible or oil-soluble or else soluble in some medium in which they can be applied to the gelling agent before incorporating the latter in the oil.

After the amine, imidazoline, inorganic gelling agent and oil have been mixed, the composition is heated to at least 300 F. This develops the thickening effect of the amine. Heating to this temperature while subjecting the composition to high shear is sufilicient to develop the effect, but a prolonged heating at a temperature above 300 F., say from a few minutes to a few hours, does no harm provided the temperature is not so high as to result in decomposition of any component of the mixture.

The composition of the invention is not limited to the oil, gelling agent, imidazoline and amine. Any of the materials conventionally added to lubricants can be included. The expression consisting essentially of as used herein is intended to refer to the components which are essential to the composition, that is, the oil, the inorganic gelling agent imidazoline and] amine, and the expression does not exclude other components from the composition which do not render it unsuitable as a hydraulic fluid.

The following examples illustrate preferred embodiments of the invention:

Examples 1 to 3 Into 87 g. of straw paraffin oil (API gravity 31.4, viscosity 74.1 SSU at F., 36.6 SSU at 210 F. ASTM slope=0.78) was mixed with 0.22 g. of Amine O (1-B-hydroxyethyl-Z-heptadecenyl imidazoline) Santocel AR (2.18 g.) silica aerogel was added with hand stirring.

A second sample was prepared employing 0.22 g. Armeen 10-D (a commercial amine mixture consisting mostly of decylamine), instead of the Amine O. A third sample was prepared adding 0.11 g. of Amine O and 0.11 g. of Armeen lO-D instead of the 0.22 g. Amine 0.

All three samples, with a control sample containing only the 2.18 g. of Santocel AR, were recycled through a small gear pump and then through a steel coil at 400 F., ejected through a diesel injector nozzle set at 2500 to 3000 p.s.i.g. into a flask, and held under a partial vacuum for a short time to remove entrained air.

The viscosities and ASTM slope of the samples were determined in a Stormer viscometer. The results were Examples 4 to 11 A second series of oils was prepared as set forth forth in Examples 1 to 3, using 0.5% and 1.5% concentrations of Santocel AR, and 0.05% and 0.10% concentrations of Amine O and of decylamine by weight of the oil. The base stock used was a solvent-extracted oil with a viscosity of 150 SSU at 100 F. and 44 SSU at 210 F. (viscosity index 95). Portions of the samples 'were allowed to stand at room temperature for 42 days after heating to 400 F. in the steel coil only and after both heating to 400 F. and atomization through the diesel injector nozzle, with the following results:

The oils containing the larger amount of Santocel *were more stable and stability was further increased as the amount of Armeen was increased. The 0.05% level 'of Amine O was better than the 0.10% level. The

stability was improved appreciably by the atomization in the case of the oils containing larger amounts of Santocel.

All parts and percentages in the specification and claims are by weight. Amounts of the amine and imidazoline are by weight of the inorganic gelling agent and amounts of the inorganic gelling agent are by weight of the oil unless otherwise indicated.

I claim: 1'. In a process for fluid power transmission the int:- provement which comprises transmitting power by' means of a fluid having a viscosity of from 75 to 1000' SSU at 100 F. and from to 750 SSU at 210 F., and

'having an ASTM slope below about 0.3, consisting essentially of a mineral lubricating oil having a viscosity of from about 50 to 330 SSU to 100 F. and from 25 to 565 SSU at 210 F., a silica aerogel in an amount within the range from about 1% to about 3% imparting an increased viscosity and a decreased ASTM slope to the oil, from about 1% to about by weight of the silica aerogel of an aliphatic amine selected from the group consisting of primary and secondary amines, the primary amines having one and the secondary amines having two aliphatic hydrocarbon radicals of from eight to twenty carbon atoms, and from about 1% to about 20% by weight of the silica aerogel of an aliphatic imidazoline having the following formula:

where R is selected from the group consisting of hydrogen, alkyl and hydroxyalkyl radicals having from one to eighteen carbon atoms and R is selected from the group consisting of alkyl and alkylene radicals having from eight to twenty carbon atoms, the amine and imidazoline imparting a further increase in viscosity and a further .de crease in ASTM slope, supplementing the efiect of the silica aerogel.

2. A process in accordance with claim 1 in which the imidazoline is 1-j3 hydroxyethyl-Z-heptadecenyl imidazo line.

3. A process in accordance with claim 1 in which the amine is decylarnine.

References Cited in the file of this patent UNITED STATES PATENTS 2,531,440 Jordan Nov. 28, 1950 2,554,222 Stross May 22, 1951 2,655,476 Hughes et a1. Oct. 13', 1953 2,711,393 Hughes et a1. June 21, 1955 2,766,205 Marshall et al Oct. 9, 1956.

UNITED STATES PATENT oEETEE CERTIFICATION OF CRECT1ON Patent N0a 2,968,623 January 17, 1961 Samuel Ma Darling It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

' Column 8, line 8 for "'to" second occurrence read ati--o ,Sig-ned and sealed this 6th day of June 1961:,

(SEAL) Attest:

' ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents 

1. IN A PROCESS FOR FLUID POWER TRANSMISSION THE IMPROVEMENT WHICH COMPRISES TRANSMITTING POWER BY MEANS OF A FLUID HAVING A VISCOSITY OF FROM 75 TO 1000 SSU AT 100*F. AND FROM 50 TO 750 SSU AT 210*F., AND HAVING AN ASTM SLOPE BETWEEN ABOUT 0.3, CONSISTING ESSENTIALLY OF A MINERAL LUBRICATING OIL HAVING A VISCOSITY OF FROM ABOUT 50 TO 330 SSU TO 100*F. AND FROM 25 TO 565 SSU AT 210*F., A SILICA AEROGEL IN AN AMOUNT WITHIN THE RANGE FROM ABOUT 1% TO ABOUT 3% IMPARTING AN INCREASED VISCOSITY AND A DECREASED ASTM SLOPE TO THE OIL, FROM ABOUT 1% TO ABOUT 60% BY WEIGHT OF THE SILICA AEROGEL OF AN ALIPHATIC AMINE SELECTED FROM THE GROUP CONSISTING OF PRIMARY AND SECONDARY AMINES, THE PRIMARY AMINES HAVING ONE AND THE SECONDARY AMINES HAVING TWO ALIPHATIC HYDROCARBON RADICALS OF FROM EIGHT TO TWENTY CARBON ATOMS, AND FROM ABOUT 1% TO ABOUT 20% BY WEIGHT OF THE SILICA AEROGEL OF AN ALIPHATIC IMIDAZONE HAVING THE FOLLOWING FORMULA: 